Mast cells are essential components of the immune system, particularly in connective tissues and the skin. Werner Syndrome (WS) is a rare, autosomal recessive disease, and individuals with the disease exhibit many pathologies observed in "normal" aging, including cataracts, atherosclerosis, diabetes, and cancer. The gene for WS, WRN, has a partial amino acid similarity to the RecQ helicase family in the central portion of the protein, suggesting that the WRN protein is a DNA and/or RNA helicase, which may participate in nucleic acid repair, replication, recombination or transcription. Potential functions of the amino- and carboxy-regions of the WRN protein are unknown. We have shown the WRN gene is highly expressed in mast cells found in the dermis of normal skin in vivo, in contrast to its comparatively low expression in multiple other tissues. This unexpected finding has led us to consider the role mast cells may play in ameliorating or contributing to the manifestations of "normal," systemic aging as well as the role the mast cell plays in the WS phenotype. In this RO-3 proposal, we wish to test two hypotheses: 1) that the loss of a functional WRN protein in WS results in aberrant connective tissue mast cell function; and, 2) that the biology of the connective tissue mast cell is altered in "normal" human aging. To test these hypotheses, we will study mast cell numbers by morphometry and by examination of markers for mast cell differentiation as well as the secretory compounds secreted from mast cells. We will study WRN gene expression by RNA in situ. Samples will include skin autopsy and biopsy specimens from WS individuals, age- and sex-matched controls and normal, healthy adult individuals from three age-groups. Our proposed experiments may open a new avenues of investigation in aging research for future studies of age-associated osteoporosis and cardiovascular disease, where the mast cell may also play a role.